1. Field of the Invention
This invention relates to a process for recovering tungsten values from a brine containing minor amounts of soluble tungsten, and more particularly, but not by way of limitation, to a process for recovering concentrated, purified tungsten values from a brine containing a minor amount of soluble tungsten and a relatively high concentration of impurities.
2. Brief Description of Prior Art
Processes have heretofore been known for producing relatively pure tungsten compounds from beneficated ores. Typical of such processes is the process disclosed in U.S. Pat. No. 4,092,400, issued to Zbranek, et al. This patent discloses a process for recovering tungsten values, in the form of ammonium paratungstate, from tungsten ores and ore concentrates, particularly wolframite ores. The process of the patent incorporates a plurality of steps for the removal of impurities and the formation of the ammonium paratungstate, including grinding, caustic leaching, filtrations, chemical treatment (including acidification for removal of silica impurities), further filtration, solvent extraction of the tungsten values, stripping of the tungsten values from the solvent solution in the form of ammonium paratungstate, and recovering the ammonium paratungstate as a product.
While numerous processes have been proposed for recovering high purity tungsten compositions from ores and ore concentrates, the largest known domestic tungsten deposit is contained in the brine of Searles Lake in California. The brine of the lake, which is utilized in other processing techniques, has been estimated to contain about 170 million pounds of tungsten values in the form of soluble tungsten at concentrations not exceeding about 70 parts per million of the tungstic oxide equivalent. Therefore, the brine of the Searles Lake represents an important source for tungsten if the tungsten can be effectively and efficiently extracted from the brine.
Chemical processes have heretofore been proposed for recovering tungsten from the Searles Lake brine. However, none of the proposed chemical processes have been economical. For example, techniques for chemically treating the brine have failed due to prohibitive operating costs. Further, attempts to precipitate tungstic acid from an acidified brine have not been economically feasible because of the large chemical requirements required to change the characteristics of the alkaline brine.
Other attempts have been made to recover tungsten from the brine of Searles Lake by the use of water-insoluble ion exchange resins, such as work done by the Bureau of Mines of the U.S. Department of the Interior and reported in the Bureau of Mines Report of Investigations/1978, entitled "Tungsten Recovery From Searles Lake Brines." Such resins are capable of selectively adsorbing the tungsten from the brine without modifying the brine with costly complexing agents or other chemicals. However, even with the advent of such ion exchange resins the tungsten values recovered from the brine are impure and the concentration of the tungsten values is relatively low. Thus, a need has long been recognized for a process for recovering concentrated, substantially pure tungsten values, such as ammonium paratungstate, from brine containing a minor amount of soluble tungsten and substantial amounts of impurities.